Yob beheaded old English player (4)
I believe the answer is:
oboe
'player' is the definition.
(I've seen this before)
'yob beheaded old english' is the wordplay.
'beheaded' means to remove the first letter (the head of the word is removed).
'old english' becomes 'oe'.
'yob' with its initial letter removed is 'ob'.
'ob'+'oe'='OBOE'
(Other definitions for oboe that I've seen before include "music producer" , "issuer of notes" , "Instrument used in 1d" , "Cor anglais in its family" , "blow it!" .)